1. Field of the Invention
The present invention generally relates to an information recording/reproducing apparatus in which a rewritable optical or a rewritable optical magnetic disk having a sector structure is used, and particularly relates to an information recording/reproducing apparatus in which it is made possible to erase data in a sector having information recorded therein even in the case where the data in the ID field of the sector cannot be read or an error is generated therein.
2. Description of the Related Art
FIG. 5 is a block diagram showing a known information recording/reproducing apparatus which comprises an information input portion 32 for receiving externally applied information to be recorded; information recording means 33 for producing a recording signal 127 modulated with the received information; an address input portion 34 for receiving an externally applied address of a sector on or from which information is recorded or reproduced; an address assignment portion 35 for assigning an address of a sector on or from which information is recorded or reproduced and for comparing the assigned address with that of a target sector to judge where there exists coincidence therebetween; a command output portion 36 for producing a writing command, a reading command and an erasing command; a gate signal generating portion 37 for generating a writing gate signal 122, a reading gate signal 125 and an erasing gate signal 123 on the basis of an ID detection signal 126 obtained when an ID field of a target sector is detected in the address assignment portion 35 and a command from the command output portion 36; information reproducing means 40 for demodulating a reproduction signal 124; an information output portion 38; and an optical disk drive 39.
FIG. 6 shows waveforms of various signals for explaining the state in which information is rewritten to be renewed in the thus arranged information recording/reproducing apparatus. Description will be made hereunder as to a case where the sector n-1, the sector n, and the sector n+1 have data A, B, and C written therein respectively, and the data B written in the sector n are substituted by data B'. The diagram (a) in FIG. 6 shows the waveform of the reproduction signal 124. First, when an address of the sector n from which the data B are to be erased is applied to the address input portion 34, an ID field (composed of address information and an error detection code thereof) of the sector n is detected by the address assignment portion 35, and the thus obtained ID detection signal 126 is applied to the gate signal generating portion 37. An erasing command is produced from the command output portion 36 and transferred to the gate signal generating portion 37, so that the erasing gate signal 123 is applied to the optical disk drive 39 at the timing as shown in the diagram (b) of FIG. 6 to cause the optical disk drive 39 to erase the data B in the sector n. The diagram (c) of FIG. 6 shows the waveform of the reproduction signal 124 after erasion in the sector n.
Next, the data B' are written into the sector n. The diagram (d) of FIG. 6 shows the waveform of the writing gate signal 122 at this time and the data B' carried by the recording signal 127 shown in the diagram (e) of FIG. 6 are written into the sector n. The diagram (f) of FIG. 6 shows the reproduction signal 124 when the data B has been substituted by the data B' in the sector n.
In such an arrangement as described above, however, it is impossible to erase data in the sector n, when an error is detected in the ID field of the sector n. FIG. 7 shows a proposal of improvement for solving this problem. An ID field of the sector n-1 preceding the sector n to be erased is detected by the address assignment portion 35 to obtain the ID detection signal 126 as shown in the diagram (b) of FIG. 7, and the erasing gate signal 123 as shown in the diagram (c) of FIG. 7 is generated by the gate signal generating portion 37 on the basis of the ID detection signal 126. This erasing gate signal 123 is delayed from the ID detection signal 126 by time t corresponding to a sector length. This proposal of the improvement has following problems.
In an optical disk mounted on the optical disk drive 39, a disc plane velocity v is deviated due to eccentricity, fluctuations in revolutional speed of a motor, vibrations, shocks, mechanical accuracy, etc., by several percents when converted into a revolutional speed thereof. Further, it may be assumed that the optical disk is accurately divided into sectors each having a sector length l by means of a cutting machine, and the time t for every sector in the reproduction signal 124 can be represented by l/v, so that the time t may be deviated by several percents.
The diagram (d) of FIG. 7 shows a deviation in pulse position in the case where the erasing gate 126 is generated at the ID field of the sector n-1. In the diagram, the jitter time at the leading and trailing edges of the erasing gate signal 123 is represented by .DELTA.t.sub.1 and .DELTA.t.sub.2 respectively, the latter being twice as long as the former. The jitter time is established so that .+-..DELTA.t.sub.1 =.+-.20 .mu.s and .+-..DELTA.t.sub.2 =.+-.42 .mu.s under the conditions that the number of revolution is 1800 rpm, the number of sectors is 32 sectors/track, and the deviation in revolutional speed is .+-.2%. Similarly to this, in recording, data are recorded with jitter time .+-..DELTA.t.sub.3 which is approximately equal to .+-..DELTA.t.sub.1. It is therefore necessary to provide gaps of a length of 15.4% of a sector, that is {2.times.(20+40+20) .mu.s/1.04ms}, in order to cause the erasing gate signal 123 to contain all the data so as not to be overlapped on the ID fields. This means a loss of 15.4% in storage capacity. Further, the jitter time causes partial differences in number of times of erasion in the gaps 1 and 2 at the leading and trailing edges of the erasing gate signal 123 on the medium of a disk, so that there has been such a disadvantage that signal processing at ID field and SYNC (synchronization) portion of data is made difficult because of disturbance in reflectance due to differences in fatigue of the medium.